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# Nitrogen Family

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 Sub Topics The elements nitrogen (N), phosphorous (P), arsenic (Ar), antimony (Sb) and bismuth (Bi) constitute group 15 or VA of periodic table. Nitrogen is very important and well known element of this group. It constitutes nearly 78.1percent by volume and 75.5 percent by weight of the air is essential constituent of fertilizers, explosives and food stuffs.After the name of the first element these elements are collectively known as nitrogen family. These elements are also known as pnictogens and their compounds pnictides which contain X3- species. Nitrogen and phosphorus are non metals arsenic and antimony are metalloids and bismuth is a metal.

## Nitrogen Group

The elements are organized and displayed on a chart called the periodic table. It is broken down into columns called groups and rows called periods. The fifteenth column of the periodic table known as group 15 contains five elements.

The nitrogen family elements are listed below.
1. Nitrogen (N)
2. Phosphorus (P)
3. Arsenic (Ar)
4. Antimony (Sb)
5. Bismuth (Bi)
This group is often called the nitrogen group.

The nitrogen group was once called the pnictogen group. This comes from the Greek word that means "to choke." The origin of this term comes from the fact that pure nitrogen can cause asphyxiation when breathed in because it does not contain the oxygen necessary to support life.

## Nitrogen Family Periodic Table

The elements nitrogen, phosphorus, arsenic, antimony and bismuth are referred to as the nitrogen family of element and occupy group V-A in the periodic table. The nitrogen family periodic table is shown below.

Nitrogen and phosphorus are non metals, arsenic is a semi metal or non metal, antimony and bismuth are metals. Their general electronic configuration is ns2np3.

## Physical Properties of Nitrogen

The physical properties of group 15 elements are given below.
1. Physical state - There is a gradual change in physical states of these elements are observed. Nitrogen is a gas, phosphorus is solid and at low temperature it can be vaporized. The other three elements are solids.
2. Metallic and non metallic character - Metallic character varies depending on the change in atomic number. Nitrogen and phosphorus are non metals whereas arsenic, antimony and bismuth are metals.
3. Allotropy - All elements exhibit allotropy except nitrogen. Phosphorus exists as white, red, scarlet and black phosphorus, arsenic exists in three forms grey, yellow and black, arsenic exists as yellow, black and explosive antimony.
4. Melting and boiling points - On moving down the group the melting and boiling points increases with increase in atomic number.
5. Density - Density also increases on moving down the group with increase in atomic number.
6. Atomic volume, atomic radius and ionic radius - All these property increases with increase in atomic number of the elements of group 15.
7. Electronegativity - it decreases on moving down the group indicating a gradual change from non metallic to metallic character.
8. Ionization energies - It decreases regularly on moving down the group due to increase in size of the atom and decreasing shielding effect of electrons from the nucleus.
9. Oxidation state - it exhibit both positive and negative oxidation state. The common oxidation state is +3. nitrogen shows +1, +2, +4 and +5 and phosphorous shows +4 oxidation state also.
10. Catenation - it is shown by all the elements of this group. as is apparent from bond energies the tendency for catenation decreases on moving down the group from nitrogen to bismuth.

## Chemical Properties of Nitrogen

The chemical properties of group 15 elements are given below.

Formation of hydride

M + H2 $\rightarrow$ MH3

All elements form MH3 type hydride. The thermal stability of hydride of this group decreases on moving down the group. This is due to the increase in atomic size. The basic nature also decreases on moving down the group because of the increase in size of the central metal atom. The melting point and boiling point goes on increasing as we move down the group due to increase in molecular size. Except ammonia (NH3) all other hydride of other elements do not exhibit hydrogen bonding. All hydride are pyramidal in shape. On moving down the group the bond angles decrease due to decrease in bond-pair-bond-pair repulsion.

Formation of oxides

M + O2 $\rightarrow$ MO2
M + O2 $\rightarrow$ M2O3

All the elements of this group form three oxides except nitrogen which forms five oxides. Nitrogen forms N2O, NO, N2O3, NO2 and N2O5. Phosphorus also forms an extensive series of sulphides and the most stable is tetra phosphorus trisulfide P4S3. The main use of this compound is it is used in strike anywhere matches. Apart for this other elements As, Sb and Bi form oxides of general formula M2O3. The oxides of nitrogen and phosphorus are acidic and arsenic and antimony are amphoteric and bismuth is basic in nature.

Formation of oxyacids

In nitrogen several oxyacids are unstable in pure state and are known only in aqueous solution or as their salts. only two are well known. One is Nitrous acid (HNO3) and the other is nitric acid (HNO3). Nitrous acid is a weak acid in aqueous solution and sodium nitrate is is mildly toxic to human beings. Nitric acid is prepared by Ostwald process. In combination with concentrated HCl aqua-regia is formed. Apart for these two hypo nitrous acid and peroxonitric acid are also called oxyacids of nitrogen. Important oxyacids of phosphorus are listed below.
1. Orthophosphoric acid - H3PO4
2. Pyrophosphoric acid - H4P2O7
3. Metaphosphoric acid - HPO3
4. Phosphonic acid - H3PO3
5. Hypophosphorys acid - H3PO2
6. Hypophosphoric acid - H4P2O6

Formation of halides

M + X (halogen) $\rightarrow$ MX3

All the elements of this group form halides of the type MX3. The most stable halides of nitrogen is NF3. Except NF3 and PF3 trihalides are hydrolyzed by water and the ease of hydrolysis decreases down the group. NCl3 is easily hydrolyzed and SbCl3 and BiCl3 are partly hydrolyzed. P and Sb form stable pentahalides but nitrogen do not form pentahalides due to absence of d-orbitals in valence shell. Bi do not form pentahalides due to inert pair effect. PCl5 is used as a chlorinating agent.

## Hydrazine

Hydrazine is a colorless fuming liquid. The odor is like ammonia. It is prepared by the oxidation of ammonia with alkaline sodium hypochlorite in the presence of gelatin.

2NH3(aq) + NaClO(aq) $\rightleftharpoons$ N2H4(aq) + NaCl(aq) + H2O(l)

Hydrazine is a strong reducing agent as reflected in the reduction potential. Hydrazine reducing ability is exploited in its use in waste water treatment for chemical plants. A related use is the treatment of water boilers in large electric generating plants.

## Hydrazoic acid

In hydrazoic acid 3 nitrogen atoms are linked together. To synthesize the acid it is therefore reasonable to start with compounds in which 2 nitrogen atoms are already bound together such as dinitrogen oxide or hydrazine.

Free hydrazoic acid can be obtained in high yield from the sodium salt by distillation with dilute sulfuric acid followed by dehydration of the distillate with calcium chloride. Hydrazine can be converted to hydrazoic acid by reaction with nitrous acid in either at 0oC in the presence of sodium methoxide which forms the sodium salt.

HNO2 + H4N2 $\rightarrow$ HN3 + 2H2O

## Hydroxylamine

Hydroxylamine is a key intermediate in nitrogen fixation. Hydroxylamine can be prepared by the reduction of hydroxylamine hydrochloride by sodium but-oxide in solution or from the oxidation of nitrogen monoxide or the hydrolysis of nitroparaffins.

It is used to prepare oximes, an important functional group. It is also an intermediate in biological nitrification. Hydroxyamine is used as a nucleophile in aromatic substitution reactions as a reducing agents and for the conversion of aldehyde to nitriles.

## Nitric Oxide

It is a colorless gas produced in the laboratory when copper metal is treated with dilute nitric acid.

3Cu(s) + 2NO3-(aq) + 8H+(aq) $\rightarrow$ 3Cu2+(aq) + 2No(g) + 4H2O(l)

Nitric oxide is also important in many biological processes where it helps transmit messages between nerve cells and kills harmful bacteria. It also helps to protect the heart from insufficient oxygen levels by dilating blood vessels.

## Nitrous Oxide

Nitrous oxide (N2O) is a colorless, sweet smelling gas obtained when molten ammonium nitrate is heated gently at about 270oC. strong heating of this compound can produce explosion.

NH4NO3(l) $\overset{Heat}{\rightarrow}$ N2O(g) + 2H2O(g)

Known as laughing gas because small dose are mildly intoxicating, nitrous oxide is used as a dental anesthetic and as a propellent for dispensing whipped cream.

## Uses of Nitrogen

Nitrogen is used for a large number of purposes. These include inerting, process, purging and pressurizing. One main use of nitrogen is inerting. Inert atmospheres are often required in processes such as polymerization, catalyst preparation and regeneration and in plant such as centrifuges and storage tanks.

In particular it may be used to dilute the concentration of a reactant such as oxygen in an oxidation process. In high pressure processes the use of nitrogen permits the use of such pressures while limiting the partial pressure of oxygen.

## Nitrogen Family Reactivity

Nitrogen is chemically the least reactive of all elements, and enters into chemical reactions only at very high temperatures. Nitrogen is considered as an inert element because nitrogen gas normally does not interact with other substances. Individual atoms of nitrogen are highly reactive.

Nitrogen is a gas at room temperature. A nitrogen molecule N2 consists of two atoms bonded by a triple covalent bond. Phosphorous on the other hand is very reactive. In general the reactivity increases on going down the group. The trend in reactivity is shown below.

## Nitrogen Family Characteristics

1. Atomic radii - Atomic radii of these elements increases in moving down the group.
2. Ionization energy - The ionization energy decreases regularly in moving down from nitrogen to bismuth.
3. Electronegativity - The electronegativity value decreases on moving down the group from nitrogen to bismuth.
4. Melting point and boiling point - Both the properties increases from nitrogen to arsenic due to increase in molecular size.
5. Metallic character - On moving down the group metallic group increases.
6. Density - This property increases down the group.